For localizing the origin(s) of cardiac arrhythmias it is common practice to measure the electric potentials located on the inner surface of the heart by electrophysiological means within the patient's heart. For example, for this purpose electrode catheters can be inserted into the heart and moved around while recording cardiac potentials during normal heart rhythm or cardiac arrhythmia. If the arrhythmia has a regular activation sequence, the timing of the electric activation measured in voltages at the site of the electrode can be integrated when moving the electrode around during the arrhythmia, to create a three dimensional map of the electric activation. By doing this, information on the localization of the source of arrhythmia(s) and mechanisms, i.e., reentry circuits, can be diagnosed to initiate or guide treatment (radiofrequency ablation).
This mapping procedure is often aided by computer systems generating three dimensional maps of catheter positions by localizing the catheter with the help of magnetic fields (the so called Carto System) or transthoracic impedances (by Localisa and NavX). Because all the points of such maps are obtained by electrode positions in contact with the cardiac surface, this mapping system is called contact mapping. It has the inherent limitation that cardiac activation can only be assessed simultaneously at the points in contact with the myocardium. Hence, an instant map of the entire cardiac activation is impossible because the entire heart chamber cannot be contacted without compromising blood circulation. An instant mapping of the simultaneous electric activation of the heart chamber, however, might be of advantage in unstable arrhythmias of short duration, rendering the mapping procedures (moving the electrode around during the arrhythmia) too long. In addition, an instant map of cardiac electric activation might be of advantage during irregular arrhythmias or arrhythmias with non-constant activation sequences that render integration of activation times from contact mapping impossible. Finally, instant maps of cardiac activation are probably also faster and easier obtained, than a contact map generated by time consuming catheters movements to different areas of the heart in all sorts of cardiac arrhythmias.
The disadvantage of contact mapping can be overcome by “non-contact mapping”, which allows for mapping cardiac activation of a heart chamber simultaneously without contact to the cardiac wall. For this purpose, for instance, a multi electrode array mounted on an inflatable balloon can be inserted into the heart. The geometry of the heart chamber is obtained either (i) by reconstruction of a contact map, which is obtained from integration of movements with an electrode catheter within the heart chamber, or (ii) by importing imaging data from computed tomography or MRI (magnetic resonance imaging).
Once the geometry of the cardiac chamber is outlined in a map the information of a simultaneous recording of cardiac farfield potentials (unipoles) by the multi electrode array can be extrapolated to the desired cardiac map using advanced mathematical methods. This non-contact mapping has the advantage that it provides the entire electric activation measured by farfield unipolar potentials either in sinus rhythm or during arrhythmia without the need for moving an electrode catheter around the cardiac chamber. This allows for a beat to beat analysis of cardiac activation and, therefore, unstable, irregular or multifocal arrhythmias can be tracked and treated. However, the disadvantage of non-contact mapping is that it relies on farfield potentials, which do not allow for the same precision in localization as contact mapping (i.e. measuring local electrograms (potentials) of cardiac activation by touching the endocardium at the site of interest with a mapping electrode).
Furthermore, non-contact mapping is more prone to artifact generation and interference from potentials generated by cardiac re-polarization and adjacent heart chambers (atria/ventricles). These drawbacks can be overcome to a certain extent with several filtering techniques. On the other hand, in many cases these drawbacks also render the localization of cardiac arrhythmias a time-consuming frustrating intervention.
Therefore, the advantages of non-contact mapping, i.e. the instant cardiac activation maps, have to be balanced against the disadvantages, i.e. the decreased spatial resolution due to recording of far field signals, filtering of artifacts, etc.
Finally, another method for the non-invasive localization of cardiac arrhythmias is body surface mapping. In this technique multiple electrodes are attached to the entire surface of the thorax and the information of the cardiac electrograms (surface ECG) is measured in voltages integrated to maps of cardiac activation. Complex mathematical methods are required in order to determine the electric activation in a heart model, for instance, one obtained from CT or MRI imaging giving information on cardiac size and orientation within the thoracic cavity.
The disadvantage of both mapping methods, i.e. contact and non-contact types, is the representation of the electric activity of the heart by means of potentials, that are the result of a summation of electric activities of many cardiac cells. The integration of all these local electric ion charges generated by the cardiac cells provides for the potentials that are measured by current mapping systems.
Therefore, it is an object of the present invention to provide a method, a system, a program and a device for improving precision, accuracy and spatial resolution of cardiac activation mapping, when compared to prior art systems.